Pressing configures one piece of plate in a predetermined shape by performing bending forming or drawing unlike casting which makes a material obtained by liquefying metal, and the like flow through a mold to form a desired shape. For this reason, for example, according to a technology, when a product having a hollow shape is formed in pressing, a pair of shapes, each of which has substantially a half of the hollow shape corresponding to the product, is formed on a blank. Herein, a portion corresponding to the half of the hollow shape which corresponds to the product is referred to as a plank piece. Then, the pair of shapes of plank pieces formed on the blank is bent so as to be fitted together into one hollow body, and the pair of the shapes of the plank pieces is matched with each other (see Patent Literature 1).